Frame identifier

Abstract

Method and system for determining the number of one or more of a sequence of M+1 consecutive OFDM frames from analysis of the designated preambles of two or more consecutive frames (m=0, 1, . . . , M; M≧1). An overlap function OF(m;k) is formed for each frame with a sequence of selected reference signals indexed by k (k=1, 2, . . . , K), dependent upon the frame number m and the index k, and a phase (sequence location corresponding to largest amplitude of overlap function) is determined. An Mth-order phase difference is computed that corresponds to frame number of one of the M+1 frames. A consistency check is provided for the phase numbers.

1. A method for determining a number of a frame in a sequence of two or more frames, the method comprising:
 receiving a sequence of at least M+1 consecutive OFDM frames, each frame having an index m, having a designated preamble wherein the designated preamble has a selected length N 1  and an associated pseudo-noise signal PN(t;m) (m=0, . . . , M; M≧1); 
 providing an overlap function OF(m;k) of the designated preambles with each of a sequence of selected reference signals, indexed by k=1, 2, . . . , K where K is a selected integer, and determining a phase φ(m) corresponding to a location of a maximum amplitude of the overlap functions OF(m;k) for each of the M+1 designated preambles of the sequence of at least M+1 consecutive OFDM frames; 
 forming a selected pth order phase difference of the phases φ(m); and 
 comparing the pth order difference with a selected table of pth order phase differences to determine a frame number of at least one frame of M+1 consecutive OFDM frames, the frame number uniquely identifying the at least one frame in the M+1 consecutive OFDM frames. 
 
     
     
       2. The method of  claim 1 , further comprising choosing p=1 and choosing said first-order phase difference to be Δ 1 (m)=φ(m+1)−φ(m). 
     
     
       3. The method of  claim 1 , further comprising choosing p= 3  and choosing said third-order phase difference to be Δ 3 (m)=φ(m+3)−3φ(m+2)+3φ(m+1)−φ(m). 
     
     
       4. The method of  claim 1 , further comprising choosing p to be an odd integer. 
     
     
       5. The method of  claim 1 , further comprising forming a linear combination
   P 
   LC(m)=Σc(p)·Δ p (m)(P≧2) 
   p=1 
 
       where c(p) are selected coefficients, at least one of which is non-zero; and
 comparing the linear combination value LC(m) with a selected table of linear combination values to determine a frame number of at least one of the M+1 frames. 
 
     
     
       6. The method of  claim 1 , further comprising providing at least two of said pseudo-noise signals, PN(t;m 1 ) and PN(t;m 2 ), as translations of each other through a relation PN(t;m 2 )=PN(t+Δt(m 1 ,m 2 )m 1 ), where Δt(m 1 ,m 2 ) is a selected time difference depending upon at least one of said indices m 1  and m 2 . 
     
     
       7. The method of  claim 1 , further comprising
 computing a first order sum Σ 1 (m=φ(m+1)+φ(m) for at least one index number m; and 
 when the sum Σ 1 (m) is not equal to at least one of the numbers +1 and −1, adjusting a value of at least said phases φ(m) and φ(m+1) so that the sum Σ 1 (m) is equal to one of the numbers +1 and −1. 
 
     
     
       8. The method of  claim 1 , further comprising choosing at least one of said selected reference signals to be an m-sequence.